This invention generally relates to electrical connectors. More particularly, the invention relates to a two-piece, electrical receptacle terminal.
Receptacle terminals exhibiting a two or multiple piece construction are well known. These terminals generally include a housing which forms a box-type receptacle, into which a spring member is mounted. A tab or pin male terminal is inserted into the housing and is biased into contact with the housing thereby ensuring that electrical contact is made and that the male terminal is not inadvertently withdrawn from the receptacle terminal. One such receptacle terminal is disclosed in U.S. Pat. No. 3,370,265.
An early generation of these two-piece terminals were constructed with both the spring member and the housing being formed from the same metal. Typically, this metal was a high conductivity metal such as copper or a copper alloy and may have been plated with tin. While being good conductors of electricity, these metals operated poorly as springs.
The above problem led to the development of a second generation of two-piece receptacle terminals in which the housing or main body was constructed of a metal exhibiting good conductivity characteristics while the spring member was constructed of a second metal having good spring characteristics. An example of a metal used for the spring member because of its high spring rate is beryllium copper. While this second generation of receptacle terminals overcame the problems of the first, either poor spring characteristics or poor conductivity characteristics, the second generation of receptacle terminals is not without limitations.
Regarding these limitations, both generations of two-piece receptacle terminals, and especially those with copper and copper alloy spring members, have exhibited a susceptibility to mechanical over-stressing or over-sizing. Over-sizing of the receptacle is caused by the insertion of a male terminal having a large or "maximum" thickness into the gap defined between the contacts of the housing and the spring member. The insertion of this thick male terminal often results in stressing of the spring member past its plastic deformation point, resulting in a failure of the spring member to fully recover its original shape. Subsequent insertion of a smaller or "minimum" thickness male terminal can then result in a loose or non-interference connection and an open circuit or thermal runaway. Furthermore, use of modular electrical systems often results in a maximum thickness male terminal being inserted into the receptacle terminal first, followed by an insertion of a minimum thickness male terminal.
Another limitation often found in two-piece receptacle terminals is thermal stress relaxation of the spring member, again, particularly with copper alloy spring members. Thermal stress relaxation, which causes a reduction in the spring rate, is gradually onset by heating of the spring member over its lifetime. This heating can be induced by ambient heating, ohmic self-heating, and usually, a combination of both.
With the above limitations in mind, it is an object of the present invention to provide for an improved two-piece receptacle terminal exhibiting a bi-metal construction. In providing the receptacle terminal, it is a further object to limit the receptacle terminal's susceptibility to over-stressing and over-sizing. Additionally, it is an object to provide a receptacle terminal which, over its lifetime, is better able to resist thermal stress relaxation. As such, a feature of the present invention is a spring member which is predisposed to return to its original "unsprung" configuration. This predisposition is evoked by the application of heat to the spring member and is in addition to the normal tendency of the spring to return to its unsprung condition.
In achieving the above objects, the present invention provides for a two-piece quick connect tab receptacle terminal which is principally composed of two elements; a main body and a spring member. The main body is formed from a metal stamping which is subsequently bent or folded into a generally rectangular housing which includes contact points for the electrical circuit. This main body is constructed from a high conductivity metal such as a copper alloy.
The second principal component of the present invention is a spring which is retained within the main body. Upon insertion of a male tab terminal, the spring biases the male terminal into contact with the electrical contact points of the main body. The spring is constructed from a second metal and, in particular, a shape memory alloy. The shape memory alloy exhibits the characteristic of being predisposed to return to its original, unsprung shape (or near original shape) during heating. Heating can be accomplished by either ambient heating, applied external heating, ohmic self-heating or a combination of these. As a result of the "memory" of the spring utilized in the present invention, the present invention is not susceptible to thermal stress relaxation; is capable of recovering from over-stressing or over-sizing; and applies an increased biasing force against the male terminal during use.
Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which this invention relates from the subsequent description of the preferred embodiments and the appended claims taken in conjunction with the accompanying drawings.